1. Field of the Invention
This invention relates to a method of and apparatus for effecting domain refinement of electrical steels and especially, but not exclusively, high-permeability grain-oriented electrical steels. In particular, but not exclusively, the invention concerns apparatus operable to produce within steel strip and sheet lines of local plastic deformation which refine the strip or sheet's domain structures and reduce power loss without causing damage to the insulation coating of the strip or sheet thereby removing the need for recoating after treatment.
2. Discussion of the Prior Art
It is known that the magnetic properties of grain-oriented electrical steels can be enhanced by processing in a known manner which effects preferential alignment of grains within the steel.
One problem associated with known techniques for producing enhanced magnetic properties is that effecting optimum grain alignment tends simultaneously to produce larger than optimum grain sizes, this resulting in higher power losses than would have been the case with smaller grain sizes and domain wall spacings.
Known techniques for effecting domain refinement by creation of artificial grain boundaries include mechanical methods, lasers or high voltage discharge systems.
Hitherto, mechanical methods have not been found to be susceptible to commercial use with the result that relatively expensive laser systems are conventionally employed commercially. A relatively inexpensive spark ablation method (high voltage discharge system) is being utilised but this system tends to be rather slow for successful commercial use.
Although domain refinement can be achieved by a method known as mechanical ball scratching in which very small balls of diameter of the order of 0.7 mm are employed which are forced into contact with the surface of a sheet under treatment, the method is difficult to maintain and operate on a commercial basis. Also, scratching of the surface of the steel occurs, and recoating of the steel after treatment is necessary.